How to implement a method for calculating a unique hash of an object in Java?

In Java, to compute a unique hash of an object, the hashCode() method is usually overridden. It is important that:

• If two objects are equal (equals() returns true), their hashes should match.
• A good hash should distribute values evenly to reduce collisions.

Example implementation for a Person class with name and age fields:

public class Person {
    private String name;
    private int age;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Person person = (Person) o;
        return age == person.age && name.equals(person.name);
    }

    @Override
    public int hashCode() {
        int result = name.hashCode();
        result = 31 * result + age;
        return result;
    }
}

This uses a simple formula with a multiplier of 31, which is widely used in Java for hash calculation.

You can also use Objects.hash() for simplification:

@Override
public int hashCode() {
    return Objects.hash(name, age);
}